diff --git a/CMakeLists.txt b/CMakeLists.txt
index aaf89d1..9c0ed8c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -378,7 +378,8 @@
   # Don't search with REQUIRED as we can continue without gflags.
   FIND_PACKAGE(Gflags)
   IF (GFLAGS_FOUND)
-    MESSAGE("-- Found Google Flags header in: ${GFLAGS_INCLUDE_DIRS}")
+    MESSAGE("-- Found Google Flags header in: ${GFLAGS_INCLUDE_DIRS}, "
+      "in namespace: ${GFLAGS_NAMESPACE}")
   ELSE (GFLAGS_FOUND)
     MESSAGE("-- Did not find Google Flags (gflags), Building without gflags "
       "- no tests or tools will be built!")
diff --git a/cmake/FindGflags.cmake b/cmake/FindGflags.cmake
index af50220..6da0b07 100644
--- a/cmake/FindGflags.cmake
+++ b/cmake/FindGflags.cmake
@@ -36,6 +36,11 @@
 # GFLAGS_FOUND: TRUE iff gflags is found.
 # GFLAGS_INCLUDE_DIRS: Include directories for gflags.
 # GFLAGS_LIBRARIES: Libraries required to link gflags.
+# GFLAGS_NAMESPACE: The namespace in which gflags is defined.  In versions of
+#                   gflags < 2.1, this was google, for versions >= 2.1 it is
+#                   by default gflags, although can be configured when building
+#                   gflags to be something else (i.e. google for legacy
+#                   compatibility).
 #
 # The following variables control the behaviour of this module:
 #
@@ -67,6 +72,7 @@
   UNSET(GFLAGS_FOUND)
   UNSET(GFLAGS_INCLUDE_DIRS)
   UNSET(GFLAGS_LIBRARIES)
+  UNSET(GFLAGS_NAMESPACE)
   # Make results of search visible in the CMake GUI if gflags has not
   # been found so that user does not have to toggle to advanced view.
   MARK_AS_ADVANCED(CLEAR GFLAGS_INCLUDE_DIR
@@ -128,6 +134,46 @@
 # if called.
 SET(GFLAGS_FOUND TRUE)
 
+# Identify what namespace gflags was built with.
+IF (GFLAGS_INCLUDE_DIR)
+  # First try the (older) google namespace.
+  INCLUDE(CheckCXXSourceCompiles)
+  # Setup include path & link library for gflags for CHECK_CXX_SOURCE_COMPILES
+  SET(CMAKE_REQUIRED_INCLUDES ${GFLAGS_INCLUDE_DIR})
+  SET(CMAKE_REQUIRED_LIBRARIES ${GFLAGS_LIBRARY})
+  CHECK_CXX_SOURCE_COMPILES(
+    "#include <gflags/gflags.h>
+     int main(int argc, char * argv[]) {
+       google::ParseCommandLineFlags(&argc, &argv, true);
+       return 0;
+     }"
+     GFLAGS_IN_GOOGLE_NAMESPACE)
+  IF (GFLAGS_IN_GOOGLE_NAMESPACE)
+    SET(GFLAGS_NAMESPACE google)
+  ELSE (GFLAGS_IN_GOOGLE_NAMESPACE)
+    # Try (newer) gflags namespace instead.
+    #
+    # Setup include path & link library for gflags for CHECK_CXX_SOURCE_COMPILES
+    SET(CMAKE_REQUIRED_INCLUDES ${GFLAGS_INCLUDE_DIR})
+    SET(CMAKE_REQUIRED_LIBRARIES ${GFLAGS_LIBRARY})
+    CHECK_CXX_SOURCE_COMPILES(
+      "#include <gflags/gflags.h>
+       int main(int argc, char * argv[]) {
+         gflags::ParseCommandLineFlags(&argc, &argv, true);
+         return 0;
+       }"
+       GFLAGS_IN_GFLAGS_NAMESPACE)
+    IF (GFLAGS_IN_GFLAGS_NAMESPACE)
+      SET(GFLAGS_NAMESPACE gflags)
+    ENDIF (GFLAGS_IN_GFLAGS_NAMESPACE)
+  ENDIF (GFLAGS_IN_GOOGLE_NAMESPACE)
+
+  IF (NOT GFLAGS_NAMESPACE)
+    GFLAGS_REPORT_NOT_FOUND(
+      "Failed to determine gflags namespace, it is not google or gflags.")
+  ENDIF (NOT GFLAGS_NAMESPACE)
+ENDIF (GFLAGS_INCLUDE_DIR)
+
 # gflags does not seem to provide any record of the version in its
 # source tree, thus cannot extract version.
 
@@ -162,11 +208,12 @@
 # Handle REQUIRED / QUIET optional arguments.
 INCLUDE(FindPackageHandleStandardArgs)
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(Gflags DEFAULT_MSG
-  GFLAGS_INCLUDE_DIRS GFLAGS_LIBRARIES)
+  GFLAGS_INCLUDE_DIRS GFLAGS_LIBRARIES GFLAGS_NAMESPACE)
 
 # Only mark internal variables as advanced if we found gflags, otherwise
 # leave them visible in the standard GUI for the user to set manually.
 IF (GFLAGS_FOUND)
   MARK_AS_ADVANCED(FORCE GFLAGS_INCLUDE_DIR
-                         GFLAGS_LIBRARY)
+                         GFLAGS_LIBRARY
+                         GFLAGS_NAMESPACE)
 ENDIF (GFLAGS_FOUND)
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index e26dc9c..62df0c0 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -70,6 +70,11 @@
 TARGET_LINK_LIBRARIES(simple_bundle_adjuster ceres)
 
 IF (GFLAGS)
+  # The CERES_GFLAGS_NAMESPACE compile definition is NOT stored in
+  # CERES_COMPILE_OPTIONS (and thus config.h) as Ceres itself does not
+  # require gflags, only the tests and examples do.
+  ADD_DEFINITIONS(-DCERES_GFLAGS_NAMESPACE=${GFLAGS_NAMESPACE})
+
   ADD_EXECUTABLE(powell powell.cc)
   TARGET_LINK_LIBRARIES(powell ceres ${GFLAGS_LIBRARIES})
 
diff --git a/examples/bundle_adjuster.cc b/examples/bundle_adjuster.cc
index 7787d93..e44ab78 100644
--- a/examples/bundle_adjuster.cc
+++ b/examples/bundle_adjuster.cc
@@ -333,7 +333,7 @@
 }  // namespace ceres
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
   if (FLAGS_input.empty()) {
     LOG(ERROR) << "Usage: bundle_adjustment_example --input=bal_problem";
diff --git a/examples/circle_fit.cc b/examples/circle_fit.cc
index 0763806..50bba74 100644
--- a/examples/circle_fit.cc
+++ b/examples/circle_fit.cc
@@ -107,7 +107,7 @@
 };
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   double x, y, r;
diff --git a/examples/denoising.cc b/examples/denoising.cc
index bfd8118..73ac476 100644
--- a/examples/denoising.cc
+++ b/examples/denoising.cc
@@ -176,8 +176,8 @@
       usage("This program denoises an image using Ceres.  Sample usage:\n");
   usage += argv[0];
   usage += " --input=<noisy image PGM file> --foe_file=<FoE file name>";
-  google::SetUsageMessage(usage);
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::SetUsageMessage(usage);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   if (FLAGS_input.empty()) {
diff --git a/examples/libmv_bundle_adjuster.cc b/examples/libmv_bundle_adjuster.cc
index 4b01202..6135c7f 100644
--- a/examples/libmv_bundle_adjuster.cc
+++ b/examples/libmv_bundle_adjuster.cc
@@ -779,7 +779,7 @@
 }  // namespace
 
 int main(int argc, char **argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   if (FLAGS_input.empty()) {
diff --git a/examples/more_garbow_hillstrom.cc b/examples/more_garbow_hillstrom.cc
index d98e57c..471eed4 100644
--- a/examples/more_garbow_hillstrom.cc
+++ b/examples/more_garbow_hillstrom.cc
@@ -337,7 +337,7 @@
 }  // namespace ceres
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   using ceres::examples::UnconstrainedSolve;
diff --git a/examples/nist.cc b/examples/nist.cc
index 607561a..8c91a29 100644
--- a/examples/nist.cc
+++ b/examples/nist.cc
@@ -566,7 +566,7 @@
 }  // namespace ceres
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
   ceres::examples::SolveNISTProblems();
   return 0;
diff --git a/examples/powell.cc b/examples/powell.cc
index c0cba02..1c2e857 100644
--- a/examples/powell.cc
+++ b/examples/powell.cc
@@ -99,7 +99,7 @@
               "Minimizer type to use, choices are: line_search & trust_region");
 
 int main(int argc, char** argv) {
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   google::InitGoogleLogging(argv[0]);
 
   double x1 =  3.0;
diff --git a/examples/robot_pose_mle.cc b/examples/robot_pose_mle.cc
index e1a1dd0..13574f1 100644
--- a/examples/robot_pose_mle.cc
+++ b/examples/robot_pose_mle.cc
@@ -271,7 +271,7 @@
 
 int main(int argc, char** argv) {
   google::InitGoogleLogging(argv[0]);
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   // Make sure that the arguments parsed are all positive.
   CHECK_GT(FLAGS_corridor_length, 0.0);
   CHECK_GT(FLAGS_pose_separation, 0.0);
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index 97d097c..1472e65 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -205,6 +205,11 @@
         ARCHIVE DESTINATION lib${LIB_SUFFIX})
 
 IF (BUILD_TESTING AND GFLAGS)
+  # The CERES_GFLAGS_NAMESPACE compile definition is NOT stored in
+  # CERES_COMPILE_OPTIONS (and thus config.h) as Ceres itself does not
+  # require gflags, only the tests and examples do.
+  ADD_DEFINITIONS(-DCERES_GFLAGS_NAMESPACE=${GFLAGS_NAMESPACE})
+
   ADD_LIBRARY(gtest gmock_gtest_all.cc gmock_main.cc)
   ADD_LIBRARY(test_util
               evaluator_test_utils.cc
diff --git a/internal/ceres/gmock_main.cc b/internal/ceres/gmock_main.cc
index 482d293..9b2f64d 100644
--- a/internal/ceres/gmock_main.cc
+++ b/internal/ceres/gmock_main.cc
@@ -63,6 +63,6 @@
   // gflags, InitGoogleTest() (called by InitGoogleMock()) must be called
   // before ParseCommandLineFlags() to handle & remove them before gflags
   // parses the remaining flags.
-  google::ParseCommandLineFlags(&argc, &argv, true);
+  CERES_GFLAGS_NAMESPACE::ParseCommandLineFlags(&argc, &argv, true);
   return RUN_ALL_TESTS();
 }